Internet Draft James Pinkerton
draft-ietf-rddp-security-10.txt Microsoft Corporation
Category: Standards Track Ellen Deleganes
Expires: December, 2006 Intel Corporation
June 2006
DDP/RDMAP Security
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Abstract
This document analyzes security issues around implementation and
use of the Direct Data Placement Protocol(DDP) and Remote Direct
Memory Access Protocol (RDMAP). It first defines an architectural
model for an RDMA Network Interface Card (RNIC), which can
implement DDP or RDMAP and DDP. The document reviews various
attacks against the resources defined in the architectural model
and the countermeasures that can be used to protect the system.
Attacks are grouped into those that can be mitigated by using
secure communication channels across the network, attacks from
Remote Peers, and attacks from Local Peers. Attack categories
include spoofing, tampering, information disclosure, denial of
service, and elevation of privilege.
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Table of Contents
1 Introduction.................................................4
2 Architectural Model..........................................7
2.1 Components...................................................8
2.2 Resources...................................................10
2.2.1 Stream Context Memory.....................................10
2.2.2 Data Buffers..............................................10
2.2.3 Page Translation Tables...................................11
2.2.4 Protection Domain (PD)....................................11
2.2.5 STag Namespace and Scope..................................12
2.2.6 Completion Queues.........................................13
2.2.7 Asynchronous Event Queue..................................13
2.2.8 RDMA Read Request Queue...................................13
2.3 RNIC Interactions...........................................14
2.3.1 Privileged Control Interface Semantics....................14
2.3.2 Non-Privileged Data Interface Semantics...................14
2.3.3 Privileged Data Interface Semantics.......................15
2.3.4 Initialization of RNIC Data Structures for Data Transfer..15
2.3.5 RNIC Data Transfer Interactions...........................16
3 Trust and Resource Sharing..................................18
4 Attacker Capabilities.......................................19
5 Attacks That Can be Mitigated With End-to-End Security......20
5.1 Spoofing....................................................20
5.1.1 Impersonation.............................................20
5.1.2 Stream Hijacking..........................................21
5.1.3 Man-in-the-Middle Attack..................................21
5.2 Tampering - Network based modification of buffer content....22
5.3 Information Disclosure - Network Based Eavesdropping........22
5.4 Specific Requirements for Security Services.................22
5.4.1 Introduction to Security Options..........................23
5.4.2 TLS is Inappropriate for DDP/RDMAP Security...............23
5.4.3 DTLS and RDDP.............................................24
5.4.4 ULPs Which Provide Security...............................24
5.4.5 Requirements for IPsec Encapsulation of DDP...............25
6 Attacks from Remote Peers...................................26
6.1 Spoofing....................................................26
6.1.1 Using an STag on a Different Stream.......................26
6.2 Tampering...................................................27
6.2.1 Buffer Overrun - RDMA Write or Read Response..............28
6.2.2 Modifying a Buffer After Indication.......................28
6.2.3 Multiple STags to access the same buffer..................29
6.3 Information Disclosure......................................29
6.3.1 Probing memory outside of the buffer bounds...............29
6.3.2 Using RDMA Read to Access Stale Data......................29
6.3.3 Accessing a Buffer After the Transfer.....................30
6.3.4 Accessing Unintended Data With a Valid STag...............30
6.3.5 RDMA Read into an RDMA Write Buffer.......................30
6.3.6 Using Multiple STags Which Alias to the Same Buffer.......31
6.4 Denial of Service (DOS).....................................31
6.4.1 RNIC Resource Consumption.................................32
6.4.2 Resource Consumption by Idle ULPs.........................32
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6.4.3 Resource Consumption By Active ULPs.......................33
6.4.3.1 Multiple Streams Sharing Receive Buffers...............33
6.4.3.2 Remote or Local Peer Attacking a Shared CQ.............35
6.4.3.3 Attacking the RDMA Read Request Queue..................37
6.4.4 Exercise of non-optimal code paths........................38
6.4.5 Remote Invalidate an STag Shared on Multiple Streams......38
6.4.6 Remote Peer attacking an Unshared CQ......................39
6.5 Elevation of Privilege......................................39
7 Attacks from Local Peers....................................40
7.1 Local ULP Attacking a Shared CQ.............................40
7.2 Local Peer Attacking the RDMA Read Request Queue............40
7.3 Local ULP Attacking the PTT & STag Mapping..................40
8 Security considerations.....................................42
9 IANA Considerations.........................................43
10 References..................................................44
10.1 Normative References......................................44
10.2 Informative References....................................44
11 Appendix A: ULP Issues for RDDP Client/Server Protocols.....46
12 Appendix B: Summary of RNIC and ULP Implementation
Requirements.....................................................50
13 Appendix C: Partial Trust Taxonomy..........................52
14 Author's Addresses..........................................54
15 Acknowledgments.............................................55
16 Full Copyright Statement....................................57
Table of Figures
Figure 1 - RDMA Security Model....................................8
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1 Introduction
RDMA enables new levels of flexibility when communicating between
two parties compared to current conventional networking practice
(e.g. a stream-based model or datagram model). This flexibility
brings new security issues that must be carefully understood when
designing Upper Layer Protocols (ULPs) utilizing RDMA and when
implementing RDMA-aware NICs (RNICs). Note that for the purposes
of this security analysis, an RNIC may implement RDMAP [RDMAP]
and DDP [DDP], or just DDP. Also, a ULP may be an application or
it may be a middleware library.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119. Additionally the security terminology defined in
[RFC2828] is used in this specification.
The document first develops an architectural model that is
relevant for the security analysis - it details components,
resources, and system properties that may be attacked in Section
2. The document uses Local Peer to represent the RDMA/DDP
protocol implementation on the local end of a Stream (implemented
with a transport protocol such as [RFC793] or [RFC2960]). The
local Upper-Layer-Protocol (ULP) is used to represent the
application or middle-ware layer above the Local Peer. The
document does not attempt to differentiate between a Remote Peer
and a Remote ULP (an RDMA/DDP protocol implementation on the
remote end of a Stream versus the application on the remote end)
for several reasons: often the source of the attack is difficult
to know for sure; and regardless of the source, the mitigations
required of the Local Peer or local ULP are the same. Thus the
document generically refers to a Remote Peer rather than trying
to further delineate the attacker.
The document then defines what resources a local ULP may share
across Streams and what resources the local ULP may share with
the Remote Peer across Streams in Section 3.
Intentional sharing of resources between multiple Streams may
imply some level of trust between the Streams. However, some
types of resource sharing have unmitigated security attacks which
would mandate not sharing a specific type of resource unless
there is some level of trust between the Streams sharing
resources.
This document defines a new term, "Partial Mutual Trust" to
address this concept:
Partial Mutual Trust - a collection of RDMAP/DDP Streams,
which represent the local and remote end points of the
Stream, which are willing to assume that the Streams from
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the collection will not perform malicious attacks against
any of the other Streams in the collection.
ULPs have explicit control of which collection of endpoints is in
a Partial Mutual Trust collection through tools discussed in
Section 13 Appendix C: Partial Trust Taxonomy.
An untrusted peer relationship is appropriate when a ULP wishes
to ensure that it will be robust and uncompromised even in the
face of a deliberate attack by its peer. For example, a single
ULP that concurrently supports multiple unrelated Streams (e.g. a
server) would presumably treat each of its peers as an untrusted
peer. For a collection of Streams which share Partial Mutual
Trust, the assumption is that any Stream not in the collection is
untrusted. For the untrusted peer, a brief list of capabilities
is enumerated in Section 4.
The rest of the document is focused on analyzing attacks and
recommending specific mitigations to the attacks. Attacks are
categorized into attacks mitigated by end-to-end security,
attacks initiated by Remote Peers, and attacks initiated by Local
Peers. For each attack, possible countermeasures are reviewed.
ULPs within a host are divided into two categories - Privileged
and Non-Privileged. Both ULP types can send and receive data and
request resources. The key differences between the two are:
The Privileged ULP is trusted by the local system to not
maliciously attack the operating environment, but it is not
trusted to optimize resource allocation globally. For
example, the Privileged ULP could be a kernel ULP, thus the
kernel presumably has in some way vetted the ULP before
allowing it to execute.
A Non-Privileged ULP's capabilities are a logical sub-set of
the Privileged ULP's. It is assumed by the local system that
a Non-Privileged ULP is untrusted. All Non-Privileged ULP
interactions with the RNIC Engine that could affect other
ULPs need to be done through a trusted intermediary that can
verify the Non-Privileged ULP requests.
The appendices provide focused summaries of this specification.
Section 11 Appendix A: ULP Issues for RDDP Client/Server
Protocols focuses on implementers of traditional client/server
protocols. Section 12 Appendix B: Summary of RNIC and ULP
Implementation Requirements summarizes all normative requirements
in this specification. Section 13 Appendix C: Partial Trust
Taxonomy provides an abstract model for categorizing trust
boundaries.
If an RDMAP/DDP protocol implementation uses the mitigations
recommended in this document, that implementation should not
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exhibit additional security vulnerabilities above and beyond
those of an implementation of the transport protocol (i.e., TCP
or SCTP) and protocols beneath it (e.g., IP) without RDMAP/DDP.
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2 Architectural Model
This section describes an RDMA architectural reference model that
is used as security issues are examined. It introduces the
components of the model, the resources that can be attacked, the
types of interactions possible between components and resources,
and the system properties which must be preserved.
Figure 1 shows the components comprising the architecture and the
interfaces where potential security attacks could be launched.
External attacks can be injected into the system from a ULP that
sits above the RNIC Interface or from the network.
The intent here is to describe high level components and
capabilities which affect threat analysis, and not focus on
specific implementation options. Also note that the architectural
model is an abstraction, and an actual implementation may choose
to subdivide its components along different boundary lines than
defined here. For example, the Privileged Resource Manager may be
partially or completely encapsulated in the Privileged ULP.
Regardless, it is expected that the security analysis of the
potential threats and countermeasures still apply.
Note that the model below is derived from several specific RDMA
implementations. A few of note are [VERBS-RDMAC], [VERBS-RDMAC-
Overview], and [INFINIBAND].
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+-------------+
| Privileged |
| Resource |
Admin| Manager | ULP Control Interface
| | || Privileged | | Non-Privileged |
| | ULP | | ULP |
| +-------------+ +-----------------+
| ^ ^
|Privileged |Privileged |Non-Privileged
|Control |Data |Data
|Interface |Interface |Interface
RNIC | | |
Interface v v v
=================================================================
+--------------------------------------+
| |
| RNIC Engine |
| |
+--------------------------------------+
^
|
v
Internet
Figure 1 - RDMA Security Model
2.1 Components
The components shown in Figure 1 - RDMA Security Model are:
* RDMA Network Interface Controller Engine (RNIC) - the
component that implements the RDMA protocol and/or DDP
protocol.
* Privileged Resource Manager - the component responsible
for managing and allocating resources associated with the
RNIC Engine. The Resource Manager does not send or
receive data. Note that whether the Resource Manager is
an independent component, part of the RNIC, or part of
the ULP is implementation dependent.
* Privileged ULP - See Section 1 Introduction for a
definition of Privileged ULP. The local host
infrastructure can enable the Privileged ULP to map a
data buffer directly from the RNIC Engine to the host
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through the RNIC Interface, but it does not allow the
Privileged ULP to directly consume RNIC Engine resources.
* Non-Privileged ULP - See Section 1 Introduction for a
definition of Non-Privileged ULP.
A design goal of the DDP and RDMAP protocols is to allow, under
constrained conditions, Non-Privileged ULP to send and receive
data directly to/from the RDMA Engine without Privileged Resource
Manager intervention - while ensuring that the host remains
secure. Thus, one of the primary goals of this document is to
analyze this usage model for the enforcement that is required in
the RNIC Engine to ensure the system remains secure.
DDP provides two mechanisms for transferring data:
* Untagged Data Transfer - the incoming payload simply
consumes the first buffer in a queue of buffers that are
in the order specified by the receiving Peer (commonly
referred to as the Receive Queue), and
* Tagged Data Transfer - the Peer transmitting the payload
explicitly states which destination buffer is targeted,
through use of an STag. STag based transfers allow the
receiving ULP to be indifferent to what order (or in what
messages) the opposite Peer sent the data, or what order
packets are received in.
Both data transfer mechanisms are also enabled through RDMAP,
with additional control semantics. Typically Tagged Data Transfer
can be used for payload transfer, while Untagged Data Transfer is
best used for control messages. However, each upper layer
protocol can determine the optimal use of tagged and untagged
messages for itself. See [APPLICABILITY] for more information on
application applicability for the two transfer mechanisms.
For DDP the two forms correspond to Untagged and Tagged DDP
Messages, respectively. For RDMAP the two forms correspond to
Send Type Messages and RDMA Messages (either RDMA Read or RDMA
Write Messages), respectively.
The host interfaces that could be exercised include:
* Privileged Control Interface - A Privileged Resource
Manager uses the RNIC Interface to allocate and manage
RNIC Engine resources, control the state within the RNIC
Engine, and monitor various events from the RNIC Engine.
It also uses this interface to act as a proxy for some
operations that a Non-Privileged ULP may require (after
performing appropriate countermeasures).
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* ULP Control Interface - A ULP uses this interface to the
Privileged Resource Manager to allocate RNIC Engine
resources. The Privileged Resource Manager implements
countermeasures to ensure that if the Non-Privileged ULP
launches an attack it can prevent the attack from
affecting other ULPs.
* Non-Privileged Data Transfer Interface - A Non-Privileged
ULP uses this interface to initiate and to check the
status of data transfer operations.
* Privileged Data Transfer Interface - A superset of the
functionality provided by the Non-Privileged Data
Transfer Interface. The ULP is allowed to directly
manipulate RNIC Engine mapping resources to map an STag
to a ULP data buffer.
If Internet control messages, such as ICMP, ARP, RIPv4, etc. are
processed by the RNIC Engine, the threat analyses for those
protocols is also applicable, but outside the scope of this
document.
2.2 Resources
This section describes the primary resources in the RNIC Engine
that could be affected if under attack. For RDMAP, all of the
defined resources apply. For DDP, all of the resources except the
RDMA Read Queue apply.
2.2.1 Stream Context Memory
The state information for each Stream is maintained in memory,
which could be located in a number of places - on the NIC, inside
RAM attached to the NIC, in host memory, or in any combination of
the three, depending on the implementation.
Stream Context Memory includes state associated with Data
Buffers. For Tagged Buffers, this includes how STag names, Data
Buffers, and Page Translation Tables (see Section 2.2.3)
interrelate. It also includes the list of Untagged Data Buffers
posted for reception of Untagged Messages (commonly called the
Receive Queue), and a list of operations to perform to send data
(commonly called the Send Queue).
2.2.2 Data Buffers
As mentioned previously, there are two different ways to expose a
local ULP's data buffers for data transfer; Untagged Data
Transfer - a buffer can be exposed for receiving RDMAP Send Type
Messages (a.k.a. DDP Untagged Messages) on DDP Queue zero - or
Tagged Data Transfer - the buffer can be exposed for remote
access through STags (a.k.a. DDP Tagged Messages). This
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distinction is important because the attacks and the
countermeasures used to protect against the attack are different
depending on the method for exposing the buffer to the network.
For the purposes of the security discussion, for Tagged Data
Transfer a single logical Data Buffer is exposed with a single
Stag on a given Stream. Actual implementations may support
scatter/gather capabilities to enable multiple physical data
buffers to be accessed with a single STag, but from a threat
analysis perspective it is assumed that a single STag enables
access to a single logical Data Buffer.
In any event, it is the responsibility of the Privileged Resource
Manager to ensure that no STag can be created that exposes memory
that the consumer had no authority to expose.
A data buffer has specific access rights. The local ULP can
control whether a data buffer is exposed for local only, or local
and remote access, and assign specific access privileges (read,
write, read and write) on a per Stream basis.
For DDP, when an STag is advertised, the Remote Peer is
presumably given write access rights to the data (otherwise there
was not much point to the advertisement). For RDMAP, when a ULP
advertises an STag, it can enable write-only, read-only, or both
write and read access rights.
Similarly, some ULPs may wish to provide a single buffer with
different access rights on a per-Stream basis. For example, some
Streams may have read-only access, some may have remote read and
write access, while on other Streams only the local ULP/Local
Peer is allowed access.
2.2.3 Page Translation Tables
Page Translation Tables are the structures used by the RNIC to be
able to access ULP memory for data transfer operations. Even
though these structures are called "Page" Translation Tables,
they may not reference a page at all - conceptually they are used
to map a ULP address space representation (e.g. a virtual
address) of a buffer to the physical addresses that are used by
the RNIC Engine to move data. If on a specific system a mapping
is not used, then a subset of the attacks examined may be
appropriate. Note that the Page Translation Table may or may not
be a shared resource.
2.2.4 Protection Domain (PD)
A Protection Domain (PD) is a local construct to the RDMA
implementation, and never visible over the wire. Protection
Domains are assigned to three of the resources of concern -
Stream Context Memory, STags associated with Page Translation
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Table entries, and data buffers. A correct implementation of a
Protection Domain requires that resources which belong to a given
Protection Domain can not be used on a resource belonging to
another Protection Domain, because Protection Domain membership
is checked by the RNIC prior to taking any action involving such
a resource. Protection Domains are therefore used to ensure that
an STag can only be used to access an associated data buffer on
one or more Streams that are associated with the same Protection
Domain as the specific STag.
If an implementation chooses to not share resources between
Streams, it is recommended that each Stream be associated with
its own, unique Protection Domain. If an implementation chooses
to allow resource sharing, it is recommended that Protection
Domain be limited to the collection of Streams that have Partial
Mutual Trust with each other.
Note that a ULP (either Privileged or Non-Privileged) can
potentially have multiple Protection Domains. This could be used,
for example, to ensure that multiple clients of a server do not
have the ability to corrupt each other. The server would allocate
a Protection Domain per client to ensure that resources covered
by the Protection Domain could not be used by another (untrusted)
client.
2.2.5 STag Namespace and Scope
The DDP specification defines a 32-bit namespace for the STag.
Implementations may vary in terms of the actual number of STags
that are supported. In any case, this is a bounded resource that
can come under attack. Depending upon STag namespace allocation
algorithms, the actual name space to attack may be significantly
less than 2^32.
The scope of an STag is the set of DDP/RDMAP Streams on which the
STag is valid. If an STag is valid on a particular DDP/RDMAP
Stream, then that stream can modify the buffer, subject to the
access rights that the stream has for the STag (see Section 2.2.2
Data Buffers for additional information).
The analysis presented in this document assumes two mechanisms
for limiting the scope of Streams for which the STag is valid:
* Protection Domain scope. The STag is valid if used on
any Stream within a specific Protection Domain, and
is invalid if used on any Stream that is not a member
of the Protection Domain.
* Single Stream scope. The STag is valid on a single
Stream, regardless of what the Stream association is
to a Protection Domain. If used on any other Stream,
it is invalid.
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2.2.6 Completion Queues
Completion Queues (CQ) are used in this document to conceptually
represent how the RNIC Engine notifies the ULP about the
completion of the transmission of data, or the completion of the
reception of data through the Data Transfer Interface
(specifically for Untagged Data Transfer - Tagged Data Transfer
can not cause a completion to occur). Because there could be many
transmissions or receptions in flight at any one time,
completions are modeled as a queue rather than a single event. An
implementation may also use the Completion Queue to notify the
ULP of other activities, for example, the completion of a mapping
of an STag to a specific ULP buffer. Completion Queues may be
shared by a group of Streams, or may be designated to handle a
specific Stream's traffic. Limiting Completion Queue association
to one, or a small number of RDMAP/DDP Streams can prevent
several forms of attacks by sharply limiting the scope of the
attack's effect.
Some implementations may allow this queue to be manipulated
directly by both Non-Privileged and Privileged ULPs.
2.2.7 Asynchronous Event Queue
The Asynchronous Event Queue is a queue from the RNIC to the
Privileged Resource Manager of bounded size. It is used by the
RNIC to notify the host of various events which might require
management action, including protocol violations, Stream state
changes, local operation errors, low water marks on receive
queues, and possibly other events.
The Asynchronous Event Queue is a resource that can be attacked
because Remote or Local Peers and/or ULPs can cause events to
occur which have the potential of overflowing the queue.
Note that an implementation is at liberty to implement the
functions of the Asynchronous Event Queue in a variety of ways,
including multiple queues or even simple callbacks. All
vulnerabilities identified are intended to apply regardless of
the implementation of the Asynchronous Event Queue. For example,
a callback function may be viewed as simply a very short queue.
2.2.8 RDMA Read Request Queue
The RDMA Read Request Queue is the memory that holds state
information for one or more RDMA Read Request Messages that have
arrived, but for which the RDMA Read Response Messages have not
yet been completely sent. Because potentially more than one RDMA
Read Request can be outstanding at one time, the memory is
modeled as a queue of bounded size. Some implementations may
enable sharing of a single RDMA Read Request Queue across
multiple Streams.
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2.3 RNIC Interactions
With RNIC resources and interfaces defined, it is now possible to
examine the interactions supported by the generic RNIC functional
interfaces through each of the 3 interfaces - Privileged Control
Interface, Privileged Data Interface, and Non-Privileged Data
Interface. As mentioned previously in Section 2.1 Components,
there are two data transfer mechanisms to be examined - Untagged
Data Transfer and Tagged Data Transfer.
2.3.1 Privileged Control Interface Semantics
Generically, the Privileged Control Interface controls the RNIC's
allocation, de-allocation, and initialization of RNIC global
resources. This includes allocation and de-allocation of Stream
Context Memory, Page Translation Tables, STag names, Completion
Queues, RDMA Read Request Queues, and Asynchronous Event Queues.
The Privileged Control Interface is also typically used for
managing Non-Privileged ULP resources for the Non-Privileged ULP
(and possibly for the Privileged ULP as well). This includes
initialization and removal of Page Translation Table resources,
and managing RNIC events (possibly managing all events for the
Asynchronous Event Queue).
2.3.2 Non-Privileged Data Interface Semantics
The Non-Privileged Data Interface enables data transfer (transmit
and receive) but does not allow initialization of the Page
Translation Table resources. However, once the Page Translation
Table resources have been initialized, the interface may enable a
specific STag mapping to be enabled and disabled by directly
communicating with the RNIC, or create an STag mapping for a
buffer that has been previously initialized in the RNIC.
For RDMAP, ULP data can be sent by one of the previously
described data transfer mechanisms - Untagged Data Transfer or
Tagged Data Transfer. Two RDMAP data transfer mechanisms are
defined, one using Untagged Data Transfer (Send Type Messages),
and one using Tagged Data Transfer (RDMA Read Responses and RDMA
Writes). ULP data reception through RDMAP can be done by
receiving Send Type Messages into buffers that have been posted
on the Receive Queue or Shared Receive Queue. Thus a Receive
Queue or Shared Receive Queue can only be affected by Untagged
Data Transfer. Data reception can also be done by receiving RDMA
Write and RDMA Read Response Messages into buffers that have
previously been exposed for external write access through
advertisement of an STag (i.e. Tagged Data Transfer).
Additionally, to cause ULP data to be pulled (read) across the
network, RDMAP uses an RDMA Read Request Message (which only
contains RDMAP control information necessary to access the ULP
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buffer to be read), to cause an RDMA Read Response Message to be
generated that contains the ULP data.
For DDP, transmitting data means sending DDP Tagged or Untagged
Messages. For data reception, DDP can receive Untagged Messages
into buffers that have been posted on the Receive Queue or Shared
Receive Queue. It can also receive Tagged DDP Messages into
buffers that have previously been exposed for external write
access through advertisement of an STag.
Completion of data transmission or reception generally entails
informing the ULP of the completed work by placing completion
information on the Completion Queue. For data reception, only an
Untagged Data Transfer can cause completion information to be put
in the Completion Queue.
2.3.3 Privileged Data Interface Semantics
The Privileged Data Interface semantics are a superset of the
Non-Privileged Data Transfer semantics. The interface can do
everything defined in the prior section, as well as
create/destroy buffer to STag mappings directly. This generally
entails initialization or clearing of Page Translation Table
state in the RNIC.
2.3.4 Initialization of RNIC Data Structures for Data Transfer
Initialization of the mapping between an STag and a Data Buffer
can be viewed in the abstract as two separate operations:
a. Initialization of the allocated Page Translation Table
entries with the location of the Data Buffer, and
b. Initialization of a mapping from an allocated STag name
to a set of Page Translation Table entry(s) or partial-
entries.
Note that an implementation may not have a Page Translation Table
(i.e. it may support a direct mapping between an STag and a Data
Buffer). If there is no Page Translation Table, then attacks
based on changing its contents or exhausting its resources are
not possible.
Initialization of the contents of the Page Translation Table can
be done by either the Privileged ULP or by the Privileged
Resource Manager as a proxy for the Non-Privileged ULP. By
definition the Non-Privileged ULP is not trusted to directly
manipulate the Page Translation Table. In general the concern is
that the Non-Privileged ULP may try to maliciously initialize the
Page Translation Table to access a buffer for which it does not
have permission.
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The exact resource allocation algorithm for the Page Translation
Table is outside the scope of this document. It may be allocated
for a specific Data Buffer, or be allocated as a pooled resource
to be consumed by potentially multiple Data Buffers, or be
managed in some other way. This document attempts to abstract
implementation dependent issues, and group them into higher level
security issues such as resource starvation and sharing of
resources between Streams.
The next issue is how an STag name is associated with a Data
Buffer. For the case of an Untagged Data Buffer (i.e. Untagged
Data Transfer), there is no wire visible mapping between an STag
and the Data Buffer. Note that there may, in fact, be an STag
which represents the buffer, if an implementation chooses to
internally represent Untagged Data Buffer using STags. However,
because the STag by definition is not visible on the wire, this
is a local host implementation specific issue which should be
analyzed in the context of a local host implementation specific
security analysis, and thus is outside the scope of this
document.
For a Tagged Data Buffer (i.e. Tagged Data Transfer), either the
Privileged ULP or the Privileged Resource Manager acting on
behalf of the Non-Privileged ULP may initialize a mapping from an
STag to a Page Translation Table, or may have the ability to
simply enable/disable an existing STag to Page Translation Table
mapping. There may also be multiple STag names which map to a
specific group of Page Translation Table entries (or sub-
entries). Specific security issues with this level of flexibility
are examined in Section 6.2.3 Multiple STags to access the same
buffer.
There are a variety of implementation options for initialization
of Page Translation Table entries and mapping an STag to a group
of Page Translation Table entries which have security
repercussions. This includes support for separation of Mapping an
STag versus mapping a set of Page Translation Table entries, and
support for ULPs directly manipulating STag to Page Translation
Table entry mappings (versus requiring access through the
Privileged Resource Manager).
2.3.5 RNIC Data Transfer Interactions
RNIC Data Transfer operations can be subdivided into send
operations and receive operations.
For send operations, there is typically a queue that enables the
ULP to post multiple operation requests to send data (referred to
as the Send Queue). Depending upon the implementation, Data
Buffers used in the operations may or may not have Page
Translation Table entries associated with them, and may or may
not have STags associated with them. Because this is a local host
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specific implementation issue rather than a protocol issue, the
security analysis of threats and mitigations is left to the host
implementation.
Receive operations are different for Tagged Data Buffers versus
Untagged Data Buffers (i.e. Tagged Data Transfer vs. Untagged
Data Transfer). For Untagged Data Transfer, if more than one
Untagged Data Buffer can be posted by the ULP, the DDP
specification requires that they be consumed in sequential order
(the RDMAP specification also requires this). Thus the most
general implementation is that there is a sequential queue of
receive Untagged Data Buffers (Receive Queue). Some
implementations may also support sharing of the sequential queue
between multiple Streams. In this case defining "sequential"
becomes non-trivial - in general the buffers for a single Stream
are consumed from the queue in the order that they were placed on
the queue, but there is no consumption order guarantee between
Streams.
For receive Tagged Data Transfer (i.e. Tagged Data Buffers, RDMA
Write Buffers, or RDMA Read Buffers), at some time prior to data
transfer, the mapping of the STag to specific Page Translation
Table entries (if present) and the mapping from the Page
Translation Table entries to the Data Buffer must have been
initialized (see Section 2.3.4 for interaction details).
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3 Trust and Resource Sharing
It is assumed that in general the Local and Remote Peer are
untrusted, and thus attacks by either should have mitigations in
place.
A separate, but related issue is resource sharing between
multiple Streams. If local resources are not shared, the
resources are dedicated on a per Stream basis. Resources are
defined in Section 2.2 Resources. The advantage of not sharing
resources between Streams is that it reduces the types of attacks
that are possible. The disadvantage of not sharing resources is
that ULPs might run out of resources. Thus there can be a strong
incentive for sharing resources, if the security issues
associated with the sharing of resources can be mitigated.
It is assumed in this document that the component that implements
the mechanism to control sharing of the RNIC Engine resources is
the Privileged Resource Manager. The RNIC Engine exposes its
resources through the RNIC Interface to the Privileged Resource
Manager. All Privileged and Non-Privileged ULPs request resources
from the Resource Manager (note that by definition both the Non-
Privileged and the Privileged application might try to greedily
consume resources, thus creating a potential Denial of Service
(DOS) attack). The Resource Manager implements resource
management policies to ensure fair access to resources. The
Resource Manager should be designed to take into account security
attacks detailed in this document. Note that for some systems the
Privileged Resource Manager may be implemented within the
Privileged ULP.
All Non-Privileged ULP interactions with the RNIC Engine that
could affect other ULPs MUST be done using the Privileged
Resource Manager as a proxy. All ULP resource allocation requests
for scarce resources MUST also be done using a Privileged
Resource Manager.
The sharing of resources across Streams should be under the
control of the ULP, both in terms of the trust model the ULP
wishes to operate under, as well as the level of resource sharing
the ULP wishes to give local processes. For more discussion on
types of trust models which combine partial trust and sharing of
resources, see Appendix C: Partial Trust Taxonomy.
The Privileged Resource Manager MUST NOT assume different Streams
share Partial Mutual Trust unless there is a mechanism to ensure
that the Streams do indeed share Partial Mutual Trust. This can
be done in several ways, including explicit notification from the
ULP that owns the Streams.
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4 Attacker Capabilities
An attacker's capabilities delimit the types of attacks that
attacker is able to launch. RDMAP and DDP require that the
initial LLP Stream (and connection) be set up prior to
transferring RDMAP/DDP Messages. This requires at least one
round-trip handshake to occur.
If the attacker is not the Remote Peer that created the initial
connection, then the attacker's capabilities can be segmented
into send only capabilities or send and receive capabilities.
Attacking with send only capabilities requires the attacker to
first guess the current LLP Stream parameters before they can
attack RNIC resources (e.g. TCP sequence number). If this class
of attacker also has receive capabilities and the ability to pose
as the receiver to the sender and the sender to the receiver,
they are typically referred to as a "man-in-the-middle" attacker
[RFC3552]. A man-in-the-middle attacker has a much wider ability
to attack RNIC resources. The breadth of attack is essentially
the same as that of an attacking Remote Peer (i.e. the Remote
Peer that setup the initial LLP Stream).
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5 Attacks That Can be Mitigated With End-to-End Security
This section describes the RDMAP/DDP attacks where the only
solution is to implement some form of end-to-end security. The
analysis includes a detailed description of each attack, what is
being attacked, and a description of the countermeasures that can
be taken to thwart the attack.
Some forms of attack involve modifying the RDMAP or DDP payload
by a network based attacker or involve monitoring the traffic to
discover private information. An effective tool to ensure
confidentiality is to encrypt the data stream through mechanisms
such as IPsec encryption. Additionally, authentication protocols
such as IPsec authentication are an effective tool to ensure the
remote entity is who they claim to be as well as ensuring that
the payload is unmodified as it traverses the network.
Note that connection setup and teardown is presumed to be done in
stream mode (i.e. no RDMA encapsulation of the payload), so there
are no new attacks related to connection setup/teardown beyond
what is already present in the LLP (e.g. TCP or SCTP). Note,
however, that RDMAP/DDP parameters may be exchanged in stream
mode, and if they are corrupted by an attacker unintended
consequences will result. Therefore, any existing mitigations for
LLP Spoofing, Tampering, Repudiation, Information Disclosure,
Denial of Service, or Elevation of Privilege continue to apply
(and are out of scope of this document). Thus the analysis in
this section focuses on attacks that are present regardless of
the LLP Stream type.
Tampering is any modification of the legitimate traffic (machine
internal or network). Spoofing attack is a special case of
tampering where the attacker falsifies an identity of the Remote
Peer (identity can be an IP address, machine name, ULP level
identity etc.).
5.1 Spoofing
Spoofing attacks can be launched by the Remote Peer, or by a
network based attacker. A network based spoofing attack applies
to all Remote Peers. This section analyzes the various types of
spoofing attacks applicable to RDMAP & DDP.
5.1.1 Impersonation
A network based attacker can impersonate a legal RDMAP/DDP Peer
(by spoofing a legal IP address). This can either be done as a
blind attack (see [RFC3552]) or by establishing an RDMAP/DDP
Stream with the victim. Because an RDMAP/DDP Stream requires an
LLP Stream to be fully initialized (e.g. for [RFC793] it is in
the ESTABLISHED state), existing transport layer protection
mechanisms against blind attacks remain in place.
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For a blind attack to succeed, it requires the attacker to inject
a valid transport layer segment (e.g. for TCP it must match at
least the 4-tuple as well as guess a sequence number within the
window) while also guessing valid RDMAP or DDP parameters. There
are many ways to attack the RDMAP/DDP protocol if the transport
protocol is assumed to be vulnerable. For example, for Tagged
Messages, this entails guessing the STag and TO values. If the
attacker wishes to simply terminate the connection, it can do so
by correctly guessing the transport & network layer values, and
providing an invalid STag. Per the DDP specification, if an
invalid STag is received, the Stream is torn down and the Remote
Peer is notified with an error. If an attacker wishes to
overwrite an Advertised Buffer, it must successfully guess the
correct STag and TO. Given that the TO often will start at zero,
this is straightforward. The value of the STag should be chosen
at random, as discussed in Section 6.1.1 Using an STag on a
Different Stream. For Untagged Messages, if the MSN is invalid
then the connection may be torn down. If it is valid, then the
receive buffers can be corrupted.
End-to-end authentication (e.g. IPsec or ULP authentication)
provides protection against either the blind attack or the
connected attack.
5.1.2 Stream Hijacking
Stream hijacking happens when a network based attacker eavesdrops
the LLP connection through the Stream establishment phase, and
waits until the authentication phase (if such a phase exists) is
completed successfully. The attacker then spoofs the IP address
and re-directs the Stream from the victim to its own machine. For
example, an attacker can wait until an iSCSI authentication is
completed successfully, and then hijack the iSCSI Stream.
The best protection against this form of attack is end-to-end
integrity protection and authentication, such as IPsec, to
prevent spoofing. Another option is to provide a physically
segregated network for security. Discussion of physical security
is out of scope for this document.
Because the connection and/or Stream itself is established by the
LLP, some LLPs are more difficult to hijack than others. Please
see the relevant LLP documentation on security issues around
connection and/or Stream hijacking.
5.1.3 Man-in-the-Middle Attack
If a network based attacker has the ability to delete or modify
packets which will still be accepted by the LLP (e.g., TCP
sequence number is correct) then the Stream can be exposed to a
man-in-the-middle attack. One style of attack is for the man-in-
the-middle to send Tagged Messages (either RDMAP or DDP). If it
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can discover a buffer that has been exposed for STag enabled
access, then the man-in-the-middle can use an RDMA Read operation
to read the contents of the associated data buffer, perform an
RDMA Write Operation to modify the contents of the associated
data buffer, or invalidate the STag to disable further access to
the buffer.
The best protection against this form of attack is end-to-end
integrity protection and authentication, such as IPsec, to
prevent spoofing or tampering. If authentication and integrity
protections are not used, then physical protection must be
employed to prevent man-in-the-middle attacks.
Because the connection/Stream itself is established by the LLP,
some LLPs are more exposed to man-in-the-middle attack than
others. Please see the relevant LLP documentation on security
issues around connection and/or Stream hijacking.
Another approach is to restrict access to only the local
subnet/link, and provide some mechanism to limit access, such as
physical security or 802.1.x. This model is an extremely limited
deployment scenario, and will not be further examined here.
5.2 Tampering - Network based modification of buffer content
This is actually a man in the middle attack - but only on the
content of the buffer, as opposed to the man in the middle attack
presented above, where both the signaling and content can be
modified. See Section 5.1.3 Man-in-the-Middle Attack.
5.3 Information Disclosure - Network Based Eavesdropping
An attacker that is able to eavesdrop on the network can read the
content of all read and write accesses to a Peer's buffers. To
prevent information disclosure, the read/written data must be
encrypted. See also Section 5.1.3 Man-in-the-Middle Attack. The
encryption can be done either by the ULP, or by a protocol that
can provide security services to RDMAP & DDP (e.g. IPsec).
5.4 Specific Requirements for Security Services
Generally speaking, Stream confidentiality protects against
eavesdropping. Stream and/or session authentication and integrity
protection is a counter measurement against various spoofing and
tampering attacks. The effectiveness of authentication and
integrity against a specific attack depend on whether the
authentication is machine level authentication (such as IPsec),
or ULP authentication.
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5.4.1 Introduction to Security Options
The following security services can be applied to an RDMAP/DDP
Stream:
1. Session confidentiality - protects against eavesdropping
(Section 5.3).
2. Per-packet data source authentication - protects against the
following spoofing attacks: network based impersonation
(Section 5.1.1), Stream hijacking (Section 5.1.2), and man in
the middle (Section 5.1.3).
3. Per-packet integrity - protects against tampering done by
network based modification of buffer content (Section 5.2)
4. Packet sequencing - protects against replay attacks, which is
a special case of the above tampering attack.
If an RDMAP/DDP Stream may be subject to impersonation attacks,
or Stream hijacking attacks, it is recommended that the Stream be
authenticated, integrity protected, and protected from replay
attacks; it may use confidentiality protection to protect from
eavesdropping (in case the RDMAP/DDP Stream traverses a public
network).
IPsec is a protocol suite which is used to secure communication
at the network layer between two peers. The IPsec protocol suite
is specified within the IP Security Architecture [RFC2401], IKE
[RFC2409], IPsec Authentication Header (AH) [RFC2402] and IPsec
Encapsulating Security Payload (ESP) [RFC2406] documents. IKE is
the key management protocol while AH and ESP are used to protect
IP traffic. Please see those RFCs for a complete description of
the respective protocols.
IPsec is capable of providing the above security services for IP
and TCP traffic respectively. ULP protocols are able to provide
only part of the above security services.
5.4.2 TLS is Inappropriate for DDP/RDMAP Security
TLS [RFC 2246] provides Stream authentication, integrity and
confidentiality for TCP based ULPs. TLS supports one-way (server
only) or mutual certificates based authentication.
If TLS is layered underneath RDMAP, there are at least two
limitations that make TLS inappropriate for DDP/RDMA security:
1. The maximum length supported by the TLS record layer protocol
is 2^14 bytes - longer packets must be fragmented (as a
comparison, the maximum length of an Untagged DDP Message is
roughly 2^32).
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2. TLS is a connection oriented protocol. If a stream cipher or
block cipher in CBC mode is used for bulk encryption, then a
packet can be decrypted only after all the packets preceding
it have already arrived. If TLS is used to protect DDP/RDMAP
traffic, then TCP must gather all out-of-order packets before
TLS can decrypt them. Only after this is done can RDMAP/DDP
place them into the ULP buffer. Thus one of the primary
features of DDP/RDMAP - enabling implementations to have a
flow-through architecture with little to no buffering, can
not be achieved if TLS is used to protect the data stream.
If TLS is layered on top of RDMAP or DDP, TLS does not protect
the RDMAP and/or DDP headers. Thus a man-in-the-middle attack can
still occur by modifying the RDMAP/DDP header to incorrectly
place the data into the wrong buffer, thus effectively corrupting
the data stream.
For these reasons, it is not RECOMMENDED that TLS be layered on
top of RDMAP or DDP.
5.4.3 DTLS and RDDP
DTLS [DTLS] provides security services for datagram protocols,
including unreliable datagram protocols. These services include
anti-replay based on a mechanism adapted from IPsec that is
intended to operate on packets as they are received from the
network. For these and other reasons, DTLS is best applied to
RDDP by employing DTLS beneath TCP, yielding a layering of RDDP
over TCP over DTLS over UDP/IP. Such a layering inserts DTLS at
roughly the same level in the protocol stack as IPsec, making
DTLS's security services an alternative to IPsec's services from
an RDDP standpoint.
For RDDP, IPsec is the better choice for a security framework,
and hence is mandatory-to-implement (as specified elsewhere in
this document). An important contributing factor to the
specification of IPsec rather than DTLS is that the non-RDDP
versions of two initial adopters of RDDP (iSCSI [iSCSI][iSER] and
NFSv4 [NFSv4][NFSv4.1]) are compatible with IPsec but neither of
these protocols currently uses either TLS or DTLS. For the
specific case of iSCSI, IPsec is the basis for mandatory-to-
implement security services [RFC3723]. Therefore this document
and the RDDP protocol specifications contain mandatory
implementation requirements for IPsec rather than for DTLS.
5.4.4 ULPs Which Provide Security
ULPs which provide integrated security but wish to leverage
lower-layer protocol security should be aware of security
concerns around correlating a specific channel's security
mechanisms to the authentication performed by the ULP. See
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[NFSv4CHANNEL] for additional information on a promising approach
called "channel binding". From [NFSv4CHANNEL]:
"The concept of channel bindings allows applications to
prove that the end-points of two secure channels at
different network layers are the same by binding
authentication at one channel to the session protection at
the other channel. The use of channel bindings allows
applications to delegate session protection to lower layers,
which may significantly improve performance for some
applications."
5.4.5 Requirements for IPsec Encapsulation of DDP
The IP Storage working group has spent significant time and
effort to define the normative IPsec requirements for IP Storage
[RFC3723]. Portions of that specification are applicable to a
wide variety of protocols, including the RDDP protocol suite. In
order to not replicate this effort, an RNIC implementation MUST
follow the requirements defined in RFC3723 Section 2.3 and
Section 5, including the associated normative references for
those sections. Note that this means that support for IPSEC ESP
mode is normative.
Additionally, since IPsec acceleration hardware may only be able
to handle a limited number of active IKE Phase 2 SAs, Phase 2
delete messages may be sent for idle SAs, as a means of keeping
the number of active Phase 2 SAs to a minimum. The receipt of an
IKE Phase 2 delete message MUST NOT be interpreted as a reason
for tearing down a DDP/RDMA Stream. Rather, it is preferable to
leave the Stream up, and if additional traffic is sent on it, to
bring up another IKE Phase 2 SA to protect it. This avoids the
potential for continually bringing Streams up and down.
Note that there are serious security issues if IPsec is not
implemented end-to-end. For example, if IPsec is implemented as a
tunnel in the middle of the network, any hosts between the Peer
and the IPsec tunneling device can freely attack the unprotected
Stream.
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6 Attacks from Remote Peers
This section describes remote attacks that are possible against
the RDMA system defined in Figure 1 - RDMA Security Model and the
RNIC Engine resources defined in Section 2.2. The analysis
includes a detailed description of each attack, what is being
attacked, and a description of the countermeasures that can be
taken to thwart the attack.
The attacks are classified into five categories: Spoofing,
Tampering, Information Disclosure, Denial of Service (DoS)
attacks, and Elevation of Privileges. As mentioned previously,
tampering is any modification of the legitimate traffic (machine
internal or network). A spoofing attack is a special case of
tampering where the attacker falsifies an identity of the Remote
Peer (identity can be an IP address, machine name, ULP level
identity etc.).
6.1 Spoofing
This section analyzes the various types of spoofing attacks
applicable to RDMAP & DDP. Spoofing attacks can be launched by
the Remote Peer, or by a network based attacker. For
countermeasures against a network based attacker, see Section 5
Attacks That Can be Mitigated With End-to-End Security.
6.1.1 Using an STag on a Different Stream
One style of attack from the Remote Peer is for it to attempt to
use STag values that it is not authorized to use. Note that if
the Remote Peer sends an invalid STag to the Local Peer, per the
DDP and RDMAP specifications, the Stream must be torn down. Thus
the threat exists if an STag has been enabled for Remote Access
on one Stream and a Remote Peer is able to use it on an unrelated
Stream. If the attack is successful, the attacker could
potentially be able to perform either RDMA Read Operations to
read the contents of the associated data buffer, perform RDMA
Write Operations to modify the contents of the associated data
buffer, or to invalidate the STag to disable further access to
the buffer.
An attempt by a Remote Peer to access a buffer with an STag on a
different Stream in the same Protection Domain may or may not be
an attack depending on whether resource sharing is intended (i.e.
whether the Streams shared Partial Mutual Trust or not). For some
ULPs, using an STag on multiple Streams within the same
Protection Domain could be desired behavior. For other ULPs,
attempting to use an STag on a different Stream could be
considered to be an attack. Since this varies by ULP, a ULP
typically would need to be able to control the scope of the STag.
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In the case where an implementation does not share resources
between Streams (including STags), this attack can be defeated by
assigning each Stream to a different Protection Domain. Before
allowing remote access to the buffer, the Protection Domain of
the Stream where the access attempt was made is matched against
the Protection Domain of the STag. If the Protection Domains do
not match, access to the buffer is denied, an error is generated,
and the RDMAP Stream associated with the attacking Stream is
terminated.
For implementations that share resources between multiple
Streams, it may not be practical to separate each Stream into its
own Protection Domain. In this case, the ULP can still limit the
scope of any of the STags to a single Stream (if it is enabling
it for remote access). If the STag scope has been limited to a
single Stream, any attempt to use that STag on a different Stream
will result in an error, and the RDMAP Stream is terminated.
Thus for implementations that do not share STags between Streams,
each Stream MUST either be in a separate Protection Domain or the
scope of an STag MUST be limited to a single Stream.
An RNIC MUST ensure that a specific Stream in a specific
Protection Domain can not access an STag in a different
Protection Domain.
An RNIC MUST ensure that if an STag is limited in scope to a
single Stream, no other Stream can use the STag.
An additional issue may be unintended sharing of STags (i.e. a
bug in the ULP) or a bug in the Remote Peer which causes an off-
by-one STag to be used. For additional protection, an
implementation should allocate STags in such a fashion that it is
difficult to predict the next allocated STag number, and also
ensure that STags are reused at as slow a rate as possible. Any
allocation method which would lead to intentional or
unintentional reuse of an STag by the peer should be avoided
(e.g. a method which always starts with a given STag and
monotonically increases it for each new allocation, or a method
which always uses the same STag for each operation).
6.2 Tampering
A Remote Peer or a network based attacker can attempt to tamper
with the contents of data buffers on a Local Peer that have been
enabled for remote write access. The types of tampering attacks
from a Remote Peer are outlined in the sections that follow. For
countermeasures against a network based attacker, see Section 5
Attacks That Can be Mitigated With End-to-End Security.
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6.2.1 Buffer Overrun - RDMA Write or Read Response
This attack is an attempt by the Remote Peer to perform an RDMA
Write or RDMA Read Response to memory outside of the valid length
range of the data buffer enabled for remote write access. This
attack can occur even when no resources are shared across
Streams. This issue can also arise if the ULP has a bug.
The countermeasure for this type of attack must be in the RNIC
implementation, leveraging the STag. When the local ULP specifies
to the RNIC the base address and the number of bytes in the
buffer that it wishes to make accessible, the RNIC must ensure
that the base and bounds check are applied to any access to the
buffer referenced by the STag before the STag is enabled for
access. When an RDMA data transfer operation (which includes an
STag) arrives on a Stream, a base and bounds byte granularity
access check must be performed to ensure the operation accesses
only memory locations within the buffer described by that STag.
Thus an RNIC implementation MUST ensure that a Remote Peer is not
able to access memory outside of the buffer specified when the
STag was enabled for remote access.
6.2.2 Modifying a Buffer After Indication
This attack can occur if a Remote Peer attempts to modify the
contents of an STag referenced buffer by performing an RDMA Write
or an RDMA Read Response after the Remote Peer has indicated to
the Local Peer or local ULP (by a variety of means) that the STag
data buffer contents are ready for use. This attack can occur
even when no resources are shared across Streams. Note that a bug
in a Remote Peer, or network based tampering, could also result
in this problem.
For example, assume the STag referenced buffer contains ULP
control information as well as ULP payload, and the ULP sequence
of operation is to first validate the control information and
then perform operations on the control information. If the Remote
Peer can perform an additional RDMA Write or RDMA Read Response
(thus changing the buffer) after the validity checks have been
completed but before the control data is operated on, the Remote
Peer could force the ULP down operational paths that were never
intended.
The local ULP can protect itself from this type of attack by
revoking remote access when the original data transfer has
completed and before it validates the contents of the buffer. The
local ULP can either do this by explicitly revoking remote access
rights for the STag when the Remote Peer indicates the operation
has completed, or by checking to make sure the Remote Peer
invalidated the STag through the RDMAP Remote Invalidate
capability (see Section 6.4.5 Remote Invalidate an STag Shared on
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Multiple Streams for a definition of Remote Invalidate), and if
it did not, the local ULP then explicitly revokes the STag remote
access rights.
The local ULP SHOULD follow the above procedure to protect the
buffer before it validates the contents of the buffer (or uses
the buffer in any way).
An RNIC MUST ensure that network packets using the STag for a
previously advertised buffer can no longer modify the buffer
after the ULP revokes remote access rights for the specific STag.
6.2.3 Multiple STags to access the same buffer
See Section 6.3.6 Using Multiple STags Which Alias to the Same
Buffer for this analysis.
6.3 Information Disclosure
The main potential source for information disclosure is through a
local buffer that has been enabled for remote access. If the
buffer can be probed by a Remote Peer on another Stream, then
there is potential for information disclosure.
The potential attacks that could result in unintended information
disclosure and countermeasures are detailed in the following
sections.
6.3.1 Probing memory outside of the buffer bounds
This is essentially the same attack as described in Section 6.2.1
Buffer Overrun - RDMA Write or Read Response, except an RDMA Read
Request is used to mount the attack. The same countermeasure
applies.
6.3.2 Using RDMA Read to Access Stale Data
If a buffer is being used for some combination of reads and
writes (either remote or local), and is exposed to a Remote Peer
with at least remote read access rights before it is initialized
with the correct data, there is a potential race condition where
the Remote Peer can view the prior contents of the buffer. This
becomes a security issue if the prior contents of the buffer were
not intended to be shared with the Remote Peer.
To eliminate this race condition, the local ULP SHOULD ensure
that no stale data is contained in the buffer before remote read
access rights are granted (this can be done by zeroing the
contents of the memory, for example). This ensures that the
Remote Peer can not access the buffer until the stale data has
been removed.
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6.3.3 Accessing a Buffer After the Transfer
If the Remote Peer has remote read access to a buffer, and by
some mechanism tells the local ULP that the transfer has been
completed, but the local ULP does not disable remote access to
the buffer before modifying the data, it is possible for the
Remote Peer to retrieve the new data.
This is similar to the attack defined in Section 6.2.2 Modifying
a Buffer After Indication. The same countermeasures apply. In
addition, the local ULP SHOULD grant remote read access rights
only for the amount of time needed to retrieve the data.
6.3.4 Accessing Unintended Data With a Valid STag
If the ULP enables remote access to a buffer using an STag that
references the entire buffer, but intends only a portion of the
buffer to be accessed, it is possible for the Remote Peer to
access the other parts of the buffer anyway.
To prevent this attack, the ULP SHOULD set the base and bounds of
the buffer when the STag is initialized to expose only the data
to be retrieved.
6.3.5 RDMA Read into an RDMA Write Buffer
One form of disclosure can occur if the access rights on the
buffer enabled remote read, when only remote write access was
intended. If the buffer contained ULP data, or data from a
transfer on an unrelated Stream, the Remote Peer could retrieve
the data through an RDMA Read operation. Note that an RNIC
implementation is not required to support STags that have both
read and write access.
The most obvious countermeasure for this attack is to not grant
remote read access if the buffer is intended to be write-only.
Then the Remote Peer would not be able to retrieve data
associated with the buffer. An attempt to do so would result in
an error and the RDMAP Stream associated with the Stream would be
terminated.
Thus if a ULP only intends a buffer to be exposed for remote
write access, it MUST set the access rights to the buffer to only
enable remote write access. Note that this requirement is not
meant to restrict the use of zero-length RDMA Reads. Zero-length
RDMA Reads do not expose ULP data. Because they are intended to
be used as a mechanism to ensure that all RDMA Writes have been
received, and do not even require a valid STag, their use is
permitted even if a buffer has only been enabled for write
access.
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6.3.6 Using Multiple STags Which Alias to the Same Buffer
Multiple STags which alias to the same buffer at the same time
can result in unintentional information disclosure if the STags
are used by different, mutually untrusted, Remote Peers. This
model applies specifically to client/server communication, where
the server is communicating with multiple clients, each of which
do not mutually trust each other.
If only read access is enabled, then the local ULP has complete
control over information disclosure. Thus a server which intended
to expose the same data (i.e. buffer) to multiple clients by
using multiple STags to the same buffer creates no new security
issues beyond what has already been described in this document.
Note that if the server did not intend to expose the same data to
the clients, it should use separate buffers for each client (and
separate STags).
When one STag has remote read access enabled and a different STag
has remote write access enabled to the same buffer, it is
possible for one Remote Peer to view the contents that have been
written by another Remote Peer.
If both STags have remote write access enabled and the two Remote
Peers do not mutually trust each other, it is possible for one
Remote Peer to overwrite the contents that have been written by
the other Remote Peer.
Thus a ULP with multiple Remote Peers which do not share Partial
Mutual Trust MUST NOT grant write access to the same buffer
through different STags. A buffer should be exposed to only one
untrusted Remote Peer at a time to ensure that no information
disclosure or information tampering occurs between peers.
6.4 Denial of Service (DOS)
A DOS attack is one of the primary security risks of RDMAP. This
is because RNIC resources are valuable and scarce, and many ULP
environments require communication with untrusted Remote Peers.
If the Remote Peer can be authenticated or the ULP payload
encrypted, clearly, the DOS profile can be reduced. For the
purposes of this analysis, it is assumed that the RNIC must be
able to operate in untrusted environments, which are open to DOS
style attacks.
Denial of service attacks against RNIC resources are not the
typical unknown party spraying packets at a random host (such as
a TCP SYN attack). Because the connection/Stream must be fully
established (e.g. a 3 message transport layer handshake has
occurred), the attacker must be able to both send and receive
messages over that connection/Stream, or be able to guess a valid
packet on an existing RDMAP Stream.
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This section outlines the potential attacks and the
countermeasures available for dealing with each attack.
6.4.1 RNIC Resource Consumption
This section covers attacks that fall into the general category
of a local ULP attempting to unfairly allocate scarce (i.e.
bounded) RNIC resources. The local ULP may be attempting to
allocate resources on its own behalf, or on behalf of a Remote
Peer. Resources that fall into this category include: Protection
Domains, Stream Context Memory, Translation and Protection
Tables, and STag namespace. These can be due to attacks by
currently active local ULPs or ones that allocated resources
earlier, but are now idle.
This type of attack can occur regardless of whether or not
resources are shared across Streams.
The allocation of all scarce resources MUST be placed under the
control of a Privileged Resource Manager. This allows the
Privileged Resource Manager to:
* prevent a local ULP from allocating more than its fair
share of resources.
* detect if a Remote Peer is attempting to launch a DOS
attack by attempting to create an excessive number of
Streams (with associated resources) and take corrective
action (such as refusing the request or applying network
layer filters against the Remote Peer).
This analysis assumes that the Resource Manager is responsible
for handing out Protection Domains, and RNIC implementations will
provide enough Protection Domains to allow the Resource Manager
to be able to assign a unique Protection Domain for each
unrelated, untrusted local ULP (for a bounded, reasonable number
of local ULPs). This analysis further assumes that the Resource
Manager implements policies to ensure that untrusted local ULPs
are not able to consume all of the Protection Domains through a
DOS attack. Note that Protection Domain consumption cannot result
from a DOS attack launched by a Remote Peer, unless a local ULP
is acting on the Remote Peer's behalf.
6.4.2 Resource Consumption by Idle ULPs
The simplest form of a DOS attack given a fixed amount of
resources is for the Remote Peer to create a RDMAP Stream to a
Local Peer, and request dedicated resources then do no actual
work. This allows the Remote Peer to be very light weight (i.e.
only negotiate resources, but do no data transfer) and consumes a
disproportionate amount of resources at the Local Peer.
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A general countermeasure for this style of attack is to monitor
active RDMAP Streams and if resources are getting low, reap the
resources from RDMAP Streams that are not transferring data and
possibly terminate the Stream. This would presumably be under
administrative control.
Refer to Section 6.4.1 for the analysis and countermeasures for
this style of attack on the following RNIC resources: Stream
Context Memory, Page Translation Tables and STag namespace.
Note that some RNIC resources are not at risk of this type of
attack from a Remote Peer because an attack requires the Remote
Peer to send messages in order to consume the resource. Receive
Data Buffers, Completion Queue, and RDMA Read Request Queue
resources are examples. These resources are, however, at risk
from a local ULP that attempts to allocate resources, then goes
idle. This could also be created if the ULP negotiates the
resource levels with the Remote Peer, which causes the Local Peer
to consume resources, however the Remote Peer never sends data to
consume them. The general countermeasure described in this
section can be used to free resources allocated by an idle Local
Peer.
6.4.3 Resource Consumption By Active ULPs
This section describes DOS attacks from Local and Remote Peers
that are actively exchanging messages. Attacks on each RDMA NIC
resource are examined and specific countermeasures are
identified. Note that attacks on Stream Context Memory, Page
Translation Tables, and STag namespace are covered in Section
6.4.1 RNIC Resource Consumption, so are not included here.
6.4.3.1 Multiple Streams Sharing Receive Buffers
The Remote Peer can attempt to consume more than its fair share
of receive data buffers (i.e. Untagged buffers for DDP are or
Send Type Messages for RDMAP) if receive buffers are shared
across multiple Streams.
If resources are not shared across multiple Streams, then this
attack is not possible because the Remote Peer will not be able
to consume more buffers than were allocated to the Stream. The
worst case scenario is that the Remote Peer can consume more
receive buffers than the local ULP allowed, resulting in no
buffers being available, which could cause the Remote Peer's
Stream to the Local Peer to be torn down, and all allocated
resources to be released.
If local receive data buffers are shared among multiple Streams,
then the Remote Peer can attempt to consume more than its fair
share of the receive buffers, causing a different Stream to be
short of receive buffers, thus possibly causing the other Stream
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to be torn down. For example, if the Remote Peer sent enough one
byte Untagged Messages, they might be able to consume all local
shared receive queue resources with little effort on their part.
One method the Local Peer could use is to recognize that a Remote
Peer is attempting to use more than its fair share of resources
and terminate the Stream (causing the allocated resources to be
released). However, if the Local Peer is sufficiently slow, it
may be possible for the Remote Peer to still mount a denial of
service attack. One countermeasure that can protect against this
attack is implementing a low-water notification. The low-water
notification alerts the ULP if the number of buffers in the
receive queue is less than a threshold.
If all of the following conditions are true, then the Local Peer
or local ULP can size the amount of local receive buffers posted
on the receive queue to ensure a DOS attack can be stopped.
* a low-water notification is enabled, and
* the Local Peer is able to bound the amount of time that
it takes to replenish receive buffers, and
* the Local Peer maintains statistics to determine which
Remote Peer is consuming buffers.
The above conditions enable the low-water notification to arrive
before resources are depleted and thus the Local Peer or local
ULP can take corrective action (e.g., terminate the Stream of the
attacking Remote Peer).
A different, but similar attack is if the Remote Peer sends a
significant number of out-of-order packets and the RNIC has the
ability to use the ULP buffer (i.e. the Untagged Buffer for DDP
or the buffer consumed by a Send Type Message for RDMAP) as a
reassembly buffer. In this case the Remote Peer can consume a
significant number of ULP buffers, but never send enough data to
enable the ULP buffer to be completed to the ULP.
An effective countermeasure is to create a high-water
notification which alerts the ULP if there is more than a
specified number of receive buffers "in process" (partially
consumed, but not completed). The notification is generated when
more than the specified number of buffers are in process
simultaneously on a specific Stream (i.e., packets have started
to arrive for the buffer, but the buffer has not yet been
delivered to the ULP).
A different countermeasure is for the RNIC Engine to provide the
capability to limit the Remote Peer's ability to consume receive
buffers on a per Stream basis. Unfortunately this requires a
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large amount of state to be tracked in each RNIC on a per Stream
basis.
Thus, if an RNIC Engine provides the ability to share receive
buffers across multiple Streams, the combination of the RNIC
Engine and the Privileged Resource Manager MUST be able to detect
if the Remote Peer is attempting to consume more than its fair
share of resources so that the Local Peer or local ULP can apply
countermeasures to detect and prevent the attack.
6.4.3.2 Remote or Local Peer Attacking a Shared CQ
For an overview of the shared CQ attack model, see Section 7.1.
The Remote Peer can attack a shared CQ by consuming more than its
fair share of CQ entries by using one of the following methods:
* The ULP protocol allows the Remote Peer to cause the
local ULP to reserve a specified number of CQ entries,
possibly leaving insufficient entries for other Streams
that are sharing the CQ.
* If the Remote Peer, Local Peer, or local ULP (or any
combination) can attack the CQ by overwhelming the CQ
with completions, then completion processing on other
Streams sharing that Completion Queue can be affected
(e.g. the Completion Queue overflows and stops
functioning).
The first method of attack can be avoided if the ULP does not
allow a Remote Peer to reserve CQ entries or there is a trusted
intermediary such as a Privileged Resource Manager. Unfortunately
it is often unrealistic to not allow a Remote Peer to reserve CQ
entries - particularly if the number of completion entries is
dependent on other ULP negotiated parameters, such as the amount
of buffering required by the ULP. Thus an implementation MUST
implement a Privileged Resource Manager to control the allocation
of CQ entries. See Section 2.1 Components for a definition of
Privileged Resource Manager.
One way that a Local or Remote Peer can attempt to overwhelm a CQ
with completions is by sending minimum length RDMAP/DDP Messages
to cause as many completions (receive completions for the Remote
Peer, send completions for the Local Peer) per second as
possible. If it is the Remote Peer attacking, and we assume that
the Local Peer's receive queue(s) do not run out of receive
buffers (if they do, then this is a different attack, documented
in Section 6.4.3.1 Multiple Streams Sharing Receive Buffers),
then it might be possible for the Remote Peer to consume more
than its fair share of Completion Queue entries. Depending upon
the CQ implementation, this could either cause the CQ to overflow
(if it is not large enough to handle all of the completions
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generated) or for another Stream to not be able to generate CQ
entries (if the RNIC had flow control on generation of CQ entries
into the CQ). In either case, the CQ will stop functioning
correctly and any Streams expecting completions on the CQ will
stop functioning.
This attack can occur regardless of whether all of the Streams
associated with the CQ are in the same Protection Domain or are
in different Protection Domains - the key issue is that the
number of Completion Queue entries is less than the number of all
outstanding operations that can cause a completion.
The Local Peer can protect itself from this type of attack using
either of the following methods:
* Size the CQ to the appropriate level, as specified below
(note that if the CQ currently exists, and it needs to be
resized, resizing the CQ is not required to succeed in
all cases, so the CQ resize should be done before sizing
the Send Queue and Receive Queue on the Stream), OR
* Grant fewer resources than the Remote Peer requested (not
supplying the number of Receive Data Buffers requested).
The proper sizing of the CQ is dependent on whether the local
ULP(s) will post as many resources to the various queues as the
size of the queue enables or not. If the local ULP(s) can be
trusted to post a number of resources that is smaller than the
size of the specific resource's queue, then a correctly sized CQ
means that the CQ is large enough to hold completion status for
all of the outstanding Data Buffers (both send and receive
buffers), or:
CQ_MIN_SIZE = SUM(MaxPostedOnEachRQ)
+ SUM(MaxPostedOnEachSRQ)
+ SUM(MaxPostedOnEachSQ)
Where:
MaxPostedOnEachRQ = the maximum number of requests which
can cause a completion that will be posted on a
specific Receive Queue.
MaxPostedOnEachSRQ = the maximum number of requests which
can cause a completion that will be posted on a
specific Shared Receive Queue.
MaxPostedOnEachSQ = the maximum number of requests which
can cause a completion that will be posted on a
specific Send Queue.
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If the local ULP must be able to completely fill the queues, or
can not be trusted to observe a limit smaller than the queues,
then the CQ must be sized to accommodate the maximum number of
operations that it is possible to post at any one time. Thus the
equation becomes:
CQ_MIN_SIZE = SUM(SizeOfEachRQ)
+ SUM(SizeOfEachSRQ)
+ SUM(SizeOfEachSQ)
Where:
SizeOfEachRQ = the maximum number of requests which
can cause a completion that can ever be posted
on a specific Receive Queue.
SizeOfEachSRQ = the maximum number of requests which
can cause a completion that can ever be posted
on a specific Shared Receive Queue.
SizeOfEachSQ = the maximum number of requests which
can cause a completion that can ever be posted
on a specific Send Queue.
Where MaxPosted*OnEach*Q and SizeOfEach*Q varies on a per Stream
or per Shared Receive Queue basis.
If the ULP is sharing a CQ across multiple Streams which do not
share Partial Mutual Trust, then the ULP MUST implement a
mechanism to ensure that the Completion Queue can not overflow.
Note that it is possible to share CQs even if the Remote Peers
accessing the CQs are untrusted if either of the above two
formulas are implemented. If the ULP can be trusted to not post
more than MaxPostedOnEachRQ, MaxPostedOnEachSRQ, and
MaxPostedOnEachSQ, then the first formula applies. If the ULP can
not be trusted to obey the limit, then the second formula
applies.
6.4.3.3 Attacking the RDMA Read Request Queue
The RDMA Read Request Queue can be attacked if the Remote Peer
sends more RDMA Read Requests than the depth of the RDMA Read
Request Queue at the Local Peer. If the RDMA Read Request Queue
is a shared resource, this could corrupt the queue. If the queue
is not shared, then the worst case is that the current Stream is
no longer functional (e.g. torn down). One approach to solving
the shared RDMA Read Request Queue would be to create thresholds,
similar to those described in Section 6.4.3.1 Multiple Streams
Sharing Receive Buffers. A simpler approach is to not share RDMA
Read Request Queue resources among Streams or enforce hard limits
of consumption per Stream. Thus RDMA Read Request Queue resource
consumption MUST be controlled by the Privileged Resource Manager
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such that RDMAP/DDP Streams which do not share Partial Mutual
Trust do not share RDMA Read Request Queue resources.
If the issue is a bug in the Remote Peer's implementation, but
not a malicious attack, the issue can be solved by requiring the
Remote Peer's RNIC to throttle RDMA Read Requests. By properly
configuring the Stream at the Remote Peer through a trusted
agent, the RNIC can be made to not transmit RDMA Read Requests
that exceed the depth of the RDMA Read Request Queue at the Local
Peer. If the Stream is correctly configured, and if the Remote
Peer submits more requests than the Local Peer's RDMA Read
Request Queue can handle, the requests would be queued at the
Remote Peer's RNIC until previous requests complete. If the
Remote Peer's Stream is not configured correctly, the RDMAP
Stream is terminated when more RDMA Read Requests arrive at the
Local Peer than the Local Peer can handle (assuming the prior
paragraph's recommendation is implemented). Thus an RNIC
implementation SHOULD provide a mechanism to cap the number of
outstanding RDMA Read Requests. The configuration of this limit
is outside the scope of this document.
6.4.4 Exercise of non-optimal code paths
Another form of DOS attack is to attempt to exercise data paths
that can consume a disproportionate amount of resources. An
example might be if error cases are handled on a "slow path"
(consuming either host or RNIC computational resources), and an
attacker generates excessive numbers of errors in an attempt to
consume these resources. Note that for most RDMAP or DDP errors,
the attacking Stream will simply be torn down. Thus for this form
of attack to be effective, the Remote Peer needs to exercise data
paths which do not cause the Stream to be torn down.
If an RNIC implementation contains "slow paths" which do not
result in the tear down of the Stream, it is recommended that an
implementation provide the ability to detect the above condition
and allow an administrator to act, including potentially
administratively tearing down the RDMAP Stream associated with
the Stream exercising data paths consuming a disproportionate
amount of resources.
6.4.5 Remote Invalidate an STag Shared on Multiple Streams
If a Local Peer has enabled an STag for remote access, the Remote
Peer could attempt to remote invalidate the STag by using the
RDMAP Send with Invalidate or Send with SE and Invalidate
Message. If the STag is only valid on the current Stream, then
the only side effect is that the Remote Peer can no longer use
the STag; thus there are no security issues.
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If the STag is valid across multiple Streams, then the Remote
Peer can prevent other Streams from using that STag by using the
remote invalidate functionality.
Thus if RDDP Streams do not share Partial Mutual Trust (i.e. the
Remote Peer may attempt to remote invalidate the STag
prematurely), the ULP MUST NOT enable an STag which would be
valid across multiple Streams.
6.4.6 Remote Peer attacking an Unshared CQ
The Remote Peer can attack an unshared CQ if the Local Peer does
not size the CQ correctly. For example, if the Local Peer enables
the CQ to handle completions of received buffers, and the receive
buffer queue is longer than the Completion Queue, then an
overflow can potentially occur. The effect on the attacker's
Stream is catastrophic. However if an RNIC does not have the
proper protections in place, then an attack to overflow the CQ
can also cause corruption and/or termination of an unrelated
Stream. Thus an RNIC MUST ensure that if a CQ overflows, any
Streams which do not use the CQ MUST remain unaffected.
6.5 Elevation of Privilege
The RDMAP/DDP Security Architecture explicitly differentiates
between three levels of privilege - Non-Privileged, Privileged,
and the Privileged Resource Manager. If a Non-Privileged ULP is
able to elevate its privilege level to a Privileged ULP, then
mapping a physical address list to an STag can provide local and
remote access to any physical address location on the node. If a
Privileged Mode ULP is able to promote itself to be a Resource
Manager, then it is possible for it to perform denial of service
type attacks where substantial amounts of local resources could
be consumed.
In general, elevation of privilege is a local implementation
specific issue and thus outside the scope of this document.
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7 Attacks from Local Peers
This section describes local attacks that are possible against
the RDMA system defined in Figure 1 - RDMA Security Model and the
RNIC Engine resources defined in Section 2.2.
7.1 Local ULP Attacking a Shared CQ
DOS attacks against a Shared Completion Queue (CQ - see Section
2.2.6 Completion Queues) can be caused by either the local ULP or
the Remote Peer if either attempts to cause more completions than
its fair share of the number of entries, thus potentially
starving another unrelated ULP such that no Completion Queue
entries are available.
A Completion Queue entry can potentially be maliciously consumed
by a completion from the Send Queue or a completion from the
Receive Queue. In the former, the attacker is the local ULP. In
the latter, the attacker is the Remote Peer.
A form of attack can occur where the local ULPs can consume
resources on the CQ. A local ULP that is slow to free resources
on the CQ by not reaping the completion status quickly enough
could stall all other local ULPs attempting to use that CQ.
For these reasons, an RNIC MUST NOT enable sharing a CQ across
ULPs that do not share Partial Mutual Trust.
7.2 Local Peer Attacking the RDMA Read Request Queue
If RDMA Read Request Queue resources are pooled across multiple
Streams, one attack is if the local ULP attempts to unfairly
allocate RDMA Read Request Queue resources for its Streams. For
example, a local ULP attempts to allocate all available resources
on a specific RDMA Read Request Queue for its Streams, thereby
denying the resource to ULPs sharing the RDMA Read Request Queue.
The same type of argument applies even if the RDMA Read Request
is not shared - but a local ULP attempts to allocate all of the
RNIC's resources when the queue is created.
Thus access to interfaces that allocate RDMA Read Request Queue
entries MUST be restricted to a trusted Local Peer, such as a
Privileged Resource Manager. The Privileged Resource Manager
SHOULD prevent a local ULP from allocating more than its fair
share of resources.
7.3 Local ULP Attacking the PTT & STag Mapping
If a Non-Privileged ULP is able to directly manipulate the RNIC
Page Translation Tables (which translate from an STag to a host
address), it is possible that the Non-Privileged ULP could point
the Page Translation Table at an unrelated Stream's or ULP's
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buffers and thereby be able to gain access to information of the
unrelated Stream/ULP.
As discussed in Section 2 Architectural Model, introduction of a
Privileged Resource Manager to arbitrate the mapping requests is
an effective countermeasure. This enables the Privileged Resource
Manager to ensure a local ULP can only initialize the Page
Translation Table (PTT)to point to its own buffers.
Thus if Non-Privileged ULPs are supported, the Privileged
Resource Manager MUST verify that the Non-Privileged ULP has the
right to access a specific Data Buffer before allowing an STag
for which the ULP has access rights to be associated with a
specific Data Buffer. This can be done when the Page Translation
Table is initialized to access the Data Buffer or when the STag
is initialized to point to a group of Page Translation Table
entries, or both.
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8 Security considerations
Please see Sections 5 Attacks That Can be Mitigated With End-to-
End Security, Section 6 Attacks from Remote Peers, and Section 7
Attacks from Local Peers, for a detailed analysis of attacks and
normative countermeasures to mitigate the attacks.
Additionally, the appendices provide a summary of the security
requirements for specific audiences. Section 11 Appendix A: ULP
Issues for RDDP Client/Server Protocols provides a summary of
implementation issues and requirements for applications which
implement a traditional client/server style of interaction. It
provides additional insight and applicability of the normative
text in Sections 5, 6, and 7. Section 12, Appendix B: Summary of
RNIC and ULP Implementation Requirements provides a convenient
summary of normative requirements for implementers.
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9 IANA Considerations
IANA considerations are not addressed by this document. Any IANA
considerations resulting from the use of DDP or RDMA must be
addressed in the relevant standards.
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10 References
10.1 Normative References
[DDP] Shah, H., J. Pinkerton, R. Recio, and P. Culley, "Direct
Data Placement over Reliable Transports", Internet-Draft Work
in Progress draft-ietf-rddp-ddp-05.txt, July 2005.
[RDMAP] Recio, R., P. Culley, D. Garcia, J. Hilland, "An RDMA
Protocol Specification", Internet-Draft Work in Progress
draft-ietf-rddp-rdmap-05.txt, July 2005.
[RFC2406] Kent, S., Atkinson, R. "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998.
[RFC2409] Harkins, D., Carrel, D., "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC2401] Kent, S., Atkinson, R. "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC2402] Kent, S., Atkinson, R. "IP Authentication Header", RFC
2402, November 1998.
[RFC3723] Aboba, B., et al, "Securing Block Storage Protocols
over IP", RFC3723, April 2004.
[RFC2960] Stewart, R. et al., "Stream Control Transmission
Protocol", RFC 2960, October 2000.
[RFC793] Postel, J., "Transmission Control Protocol - DARPA
Internet Program Protocol Specification", RFC 793, September
1981.
10.2 Informative References
[RFC2828] Shirley, R., "Internet Security Glossary", FYI 36, RFC
2828, May 2000.
[APPLICABILITY] Bestler, C. , Coene, L. "Applicability of Remote
Direct Memory Access Protocol (RDMA) and Direct Data
Placement (DDP)", Internet-Draft Work in Progress draft-ietf-
rddp-applicability-06.txt, April 2006.
[IPv6-Trust] Nikander, P., J.Kempf, E. Nordmark, "IPv6 Neighbor
Discovery Trust Models and threats", Informational RFC,
RFC3756, May 2004.
[NFSv4CHANNEL] Williams, N., "On the Use of Channel Bindings to
Secure Channels", Internet-Draft draft-ietf-nfsv4-channel-
bindings-02.txt, July 2004.
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[VERBS-RDMAC] "RDMA Protocol Verbs Specification", RDMA
Consortium standard, April 2003.
http://www.rdmaconsortium.org/home/draft-hilland-iwarp-verbs-
v1.0-RDMAC.pdf
[VERBS-RDMAC-Overview] "RDMA enabled NIC (RNIC) Verbs Overview",
slide presentation by Renato Recio, April 2003.
http://www.rdmaconsortium.org/home/RNIC_Verbs_Overview2.pdf
[RFC3552] "Guidelines for Writing RFC Text on Security
Considerations", Best Current Practice RFC, RFC 3552, July
2003.
[INFINIBAND] "InfiniBand Architecture Specification Volume 1",
release 1.2, InfiniBand Trade Association standard.
http://www.infinibandta.org/specs. Verbs are documented in
chapter 11.
[DTLS] E. Rescorla and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[iSCSI] J. Satran, et al, "Internet Small Computer Systems
Interface (iSCSI)", RFC 3720, April 2004.
[ISER] M. Ko, et al, "iSCSI Extensions for RDMA Specification",
Internet-Draft Work in Progress draft-ietf-ips-iser-05.txt,
October 2005.
[NFSv4] S. Shepler, et al, "Network File System (NFS) version 4
Protocol", RFC 3530, April 2003.
[NFSv4.1] S. Shepler, ed., "NFSv4 Minor Version 1", Internet-
Draft draft-ietf-nfsv4-minorversion1-03.txt, Work in
Progress, June 2006.
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11 Appendix A: ULP Issues for RDDP Client/Server Protocols
This section is a normative appendix to the document that is
focused on client/server ULP implementation requirements to
ensure a secure server implementation.
The prior sections outlined specific attacks and their
countermeasures. This section summarizes the attacks and
countermeasures that have been defined in the prior section which
are applicable to creation of a secure ULP (e.g. application)
server. A ULP server is defined as a ULP which must be able to
communicate with many clients which do not necessarily have a
trust relationship with each other, and ensure that each client
can not attack another client through server interactions.
Further, the server may wish to use multiple Streams to
communicate with a specific client, and those Streams may share
mutual trust. Note that this section assumes a compliant RNIC and
Privileged Resource Manager implementation - thus it focuses
specifically on ULP server (e.g. application) implementation
issues.
All of the prior section's details on attacks and countermeasures
apply to the server, thus requirements which are repeated in this
section use non-normative "must", "should", "may". In some cases
normative SHOULD statements for the ULP from the main body of
this document are made MUST statements for the ULP server because
the operating conditions can be refined to make the motives for a
SHOULD inapplicable. If a prior SHOULD is changed to a MUST in
this section, it is explicitly noted and it uses upper-case
normative statements.
The following list summarizes the relevant attacks that clients
can mount on the shared server, by re-stating the previous
normative statements to be client/server specific. Note that each
client/server ULP may employ explicit RDMA operations (RDMA Read,
RDMA Write) in differing fashions. Therefore where appropriate,
"Local ULP", "Local Peer" and "Remote Peer" are used in place of
"server" or "client", in order to retain full generality of each
requirement.
* Spoofing
* Sections 5.1.1 to 5.1.3. For protection against many
forms of spoofing attacks, enable IPsec.
* Section 6.1.1 Using an STag on a Different Stream. To
ensure that one client can not access another
client's data via use of the other client's STag, the
server ULP must either scope an STag to a single
Stream or use a unique Protection Domain per client.
If a single client has multiple Streams that share
Partial Mutual Trust, then the STag can be shared
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between the associated Streams by using a single
Protection Domain among the associated Streams (see
Section 5.4.4 ULPs Which Provide Security for
additional issues). To prevent unintended sharing of
STags within the associated Streams, a server ULP
should use STags in such a fashion that it is
difficult to predict the next allocated STag number.
* Tampering
* 6.2.2 Modifying a Buffer After Indication. Before the
local ULP operates on a buffer that was written by
the Remote Peer using an RDMA Write or RDMA Read, the
local ULP MUST ensure the buffer can no longer be
modified, by invalidating the STag for remote access
(note that this is stronger than the SHOULD in
Section 6.2.2). This can either be done explicitly by
revoking remote access rights for the STag when the
Remote Peer indicates the operation has completed, or
by checking to make sure the Remote Peer Invalidated
the STag through the RDMAP Invalidate capability, and
if it did not, the local ULP then explicitly revoking
the STag remote access rights.
* Information Disclosure
* 6.3.2 Using RDMA Read to Access Stale Data. In a
general purpose server environment there is no
compelling rationale to not require a buffer to be
initialized before remote read is enabled (and an
enormous down side of unintentionally sharing data).
Thus a local ULP MUST (this is stronger than the
SHOULD in Section 6.3.2) ensure that no stale data is
contained in a buffer before remote read access
rights are granted to a Remote Peer (this can be done
by zeroing the contents of the memory, for example).
* 6.3.3 Accessing a Buffer After the Transfer. This
mitigation is already covered by Section 6.2.2
(above).
* 6.3.4 Accessing Unintended Data With a Valid STag.
The ULP must set the base and bounds of the buffer
when the STag is initialized to expose only the data
to be retrieved.
* 6.3.5 RDMA Read into an RDMA Write Buffer. If a peer
only intends a buffer to be exposed for remote write
access, it must set the access rights to the buffer
to only enable remote write access.
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* 6.3.6 Using Multiple STags Which Alias to the Same
Buffer. The requirement in Section 6.1.1 (above)
mitigates this attack. A server buffer is exposed to
only one client at a time to ensure that no
information disclosure or information tampering
occurs between peers.
* 5.3 - Network Based Eavesdropping. Confidentiality
services should be enabled by the ULP if this threat
is a concern.
* Denial of Service
* 6.4.3.1 Multiple Streams Sharing Receive Buffers. ULP
memory footprint size can be important for some
server ULPs. If a server ULP is expecting significant
network traffic from multiple clients, using a
receive buffer queue per Stream where there is a
large number of Streams can consume substantial
amounts of memory. Thus a receive queue that can be
shared by multiple Streams is attractive.
However, because of the attacks outlined in this
section, sharing a single receive queue between
multiple clients must only be done if a mechanism is
in place to ensure one client cannot consume receive
buffers in excess of its limits, as defined by each
ULP. For multiple Streams within a single client ULP
(which presumably shared Partial Mutual Trust) this
added overhead may be avoided.
* 7.1 Local ULP Attacking a Shared CQ. The normative
RNIC mitigations require the RNIC to not enable
sharing of a CQ if the local ULPs do not share
Partial Mutual Trust. Thus while the ULP is not
allowed to enable this feature in an unsafe mode, if
the two local ULPs share Partial Mutual Trust, they
must behave in the following manner:
1) The sizing of the completion queue is based on the
size of the receive queue and send queues as
documented in 6.4.3.2 Remote or Local Peer Attacking
a Shared CQ.
2) The local ULP ensures that CQ entries are reaped
frequently enough to adhere to Section 6.4.3.2's
rules.
* 6.4.3.2 Remote or Local Peer Attacking a Shared CQ.
There are two mitigations specified in this section -
one requires a worst-case size of the CQ, and can be
implemented entirely within the Privileged Resource
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Manager. The second approach requires cooperation
with the local ULP server (to not post too many
buffers), and enables a smaller CQ to be used.
In some server environments, partial trust of the
server ULP (but not the clients) is acceptable, thus
the smaller CQ fully mitigates the remote attacker.
In other environments, the local server ULP could
also contain untrusted elements which can attack the
local machine (or have bugs). In those environments,
the worst-case size of the CQ must be used.
* 6.4.3.3 The section requires a server's Privileged
Resource Manager to not allow sharing of RDMA Read
Request Queues across multiple Streams that do not
share Partial Mutual Trust, for a ULP which performs
RDMA Read operations to server buffers. However,
because the server ULP knows best which of its
Streams share Partial Mutual Trust, this requirement
can be reflected back to the ULP. The ULP (i.e.
server) requirement in this case is that it MUST NOT
allow RDMA Read Request Queues to be shared between
ULPs which do not have Partial Mutual Trust.
* 6.4.5 Remote Invalidate an STag Shared on Multiple
Streams. This mitigation is already covered by
Section 6.2.2 (above).
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12 Appendix B: Summary of RNIC and ULP Implementation Requirements
This appendix is informative.
Below is a summary of implementation requirements for the RNIC:
* 3 Trust and Resource Sharing
* 5.4.5 Requirements for IPsec Encapsulation of DDP
* 6.1.1 Using an STag on a Different Stream
* 6.2.1 Buffer Overrun - RDMA Write or Read Response
* 6.2.2 Modifying a Buffer After Indication
* 6.4.1 RNIC Resource Consumption
* 6.4.3.1 Multiple Streams Sharing Receive Buffers
* 6.4.3.2 Remote or Local Peer Attacking a Shared CQ
* 6.4.3.3 Attacking the RDMA Read Request Queue
* 6.4.6 Remote Peer attacking an Unshared CQ.
* 6.5 Elevation of Privilege 39
* 7.1 Local ULP Attacking a Shared CQ
* 7.3 Local ULP Attacking the PTT & STag Mapping
Below is a summary of implementation requirements for the ULP
above the RNIC:
* 5.3 Information Disclosure - Network Based Eavesdropping
* 6.1.1 Using an STag on a Different Stream
* 6.2.2 Modifying a Buffer After Indication
* 6.3.2 Using RDMA Read to Access Stale Data
* 6.3.3 Accessing a Buffer After the Transfer
* 6.3.4 Accessing Unintended Data With a Valid STag
* 6.3.5 RDMA Read into an RDMA Write Buffer
* 6.3.6 Using Multiple STags Which Alias to the Same Buffer
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* 6.4.5 Remote Invalidate an STag Shared on Multiple
Streams
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13 Appendix C: Partial Trust Taxonomy
This appendix is informative.
Partial Trust is defined as when one party is willing to assume
that another party will refrain from a specific attack or set of
attacks, the parties are said to be in a state of Partial Trust.
Note that the partially trusted peer may attempt a different set
of attacks. This may be appropriate for many ULPs where any
adverse effects of the betrayal is easily confined and does not
place other clients or ULPs at risk.
The Trust Models described in this section have three primary
distinguishing characteristics. The Trust Model refers to a local
ULP and Remote Peer, which are intended to be the local and
remote ULP instances communicating via RDMA/DDP.
* Local Resource Sharing (yes/no) - When local resources
are shared, they are shared across a grouping of
RDMAP/DDP Streams. If local resources are not shared, the
resources are dedicated on a per Stream basis. Resources
are defined in Section 2.2 - Resources. The advantage of
not sharing resources between Streams is that it reduces
the types of attacks that are possible. The disadvantage
is that ULPs might run out of resources.
* Local Partial Trust (yes/no) - Local Partial Trust is
determined based on whether the local grouping of
RDMAP/DDP Streams (which typically equates to one ULP or
group of ULPs) mutually trust each other to not perform a
specific set of attacks.
* Remote Partial Trust (yes/no) - The Remote Partial Trust
level is determined based on whether the local ULP of a
specific RDMAP/DDP Stream partially trusts the Remote
Peer of the Stream (see the definition of Partial Trust
in Section 1 Introduction).
Not all of the combinations of the trust characteristics are
expected to be used by ULPs. This document specifically analyzes
five ULP Trust Models that are expected to be in common use. The
Trust Models are as follows:
* NS-NT - Non-Shared Local Resources, no Local Trust, no
Remote Trust - typically a server ULP that wants to run
in the safest mode possible. All attack mitigations are
in place to ensure robust operation.
* NS-RT - Non-Shared Local Resources, no Local Trust,
Remote Partial Trust - typically a peer-to-peer ULP,
which has, by some method outside of the scope of this
document, authenticated the Remote Peer. Note that unless
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some form of key based authentication is used on a per
RDMA/DDP Stream basis, it may not be possible be possible
for man-in-the-middle attacks to occur.
* S-NT - Shared Local Resources, no Local Trust, no Remote
Trust - typically a server ULP that runs in an untrusted
environment where the amount of resources required is
either too large or too dynamic to dedicate for each
RDMAP/DDP Stream.
* S-LT - Shared Local Resources, Local Partial Trust, no
Remote Trust - typically a ULP, which provides a session
layer and uses multiple Streams, to provide additional
throughput or fail-over capabilities. All of the Streams
within the local ULP partially trust each other, but do
not trust the Remote Peer. This trust model may be
appropriate for embedded environments.
* S-T - Shared Local Resources, Local Partial Trust, Remote
Partial Trust - typically a distributed application, such
as a distributed database application or a High
Performance Computer (HPC) application, which is intended
to run on a cluster. Due to extreme resource and
performance requirements, the application typically
authenticates with all of its peers and then runs in a
highly trusted environment. The application peers are all
in a single application fault domain and depend on one
another to be well-behaved when accessing data
structures. If a trusted Remote Peer has an
implementation defect that results in poor behavior, the
entire application could be corrupted.
Models NS-NT and S-NT above are typical for Internet networking -
neither local ULPs nor the Remote Peer is trusted. Sometimes
optimizations can be done that enable sharing of Page Translation
Tables across multiple local ULPs, thus Model S-LT can be
advantageous. Model S-T is typically used when resource scaling
across a large parallel ULP makes it infeasible to use any other
model. Resource scaling issues can either be due to performance
around scaling or because there simply are not enough resources.
Model NS-RT is probably the least likely model to be used, but is
presented for completeness.
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14 Author's Addresses
James Pinkerton
Microsoft Corporation
One Microsoft Way
Redmond, WA. 98052 USA
Phone: +1 (425) 705-5442
Email: jpink@windows.microsoft.com
Ellen Deleganes
Intel Corporation
MS JF5-355
2111 NE 25th Ave.
Hillsboro, OR 97124 USA
Phone: +1 (503) 712-4173
Email: ellen.m.deleganes@intel.com
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15 Acknowledgments
Sara Bitan
Microsoft Corporation
Email: sarab@microsoft.com
Allyn Romanow
Cisco Systems
170 W Tasman Drive
San Jose, CA 95134 USA
Phone: +1 408 525 8836
Email: allyn@cisco.com
Catherine Meadows
Naval Research Laboratory
Code 5543
Washington, DC 20375
Email: meadows@itd.nrl.navy.mil
Patricia Thaler
Agilent Technologies, Inc.
1101 Creekside Ridge Drive, #100
M/S-RG10
Roseville, CA 95678
Phone: +1-916-788-5662
email: pat_thaler@agilent.com
James Livingston
NEC Solutions (America), Inc.
7525 166th Ave. N.E., Suite D210
Redmond, WA 98052-7811
Phone: +1 (425) 897-2033
Email: james.livingston@necsam.com
John Carrier
Adaptec, Inc.
691 S. Milpitas Blvd.
Milpitas, CA 95035 USA
Phone: +1 (360) 378-8526
Email: john_carrier@adaptec.com
Caitlin Bestler
Broadcom
49 Discovery
Irvine, CA 92618
Email: cait@asomi.com
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA. 98052 USA
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Phone: +1 (425) 706-6606
Email: bernarda@windows.microsoft.com
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16 Full Copyright Statement
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This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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